Hemophilia A and B are rare bleeding disorders caused by mutations in the factor VIII (FVIII) and IX (FIX) genes. Frequency and severity of bleeding symptoms are correlated with clotting factor levels and treatment is primarily based on replacing the missing factor. Over the past decade, a new generation of FVIII and FIX recombinant products with extended plasma half-life (EHL) have been introduced. These new products have improved the quality of life of patients by reducing injection frequency for prophylaxis and increasing trough levels. The modifications of these new factor products may however induce discrepancies in results between chromogenic and onestage clotting assays, and between the various available one-stage clotting assays, and may not reflect the actual factor level.
In the information letter below, we aim at providing guidance on which STAGO reagent is the best suited for laboratory monitoring of FVIII or FIX depending on the recombinant EHL product being used. The proposals are based on the European Medicines Agency summary of product characteristics (SPC), guidelines from scientific societies, and data published in the literature or presented at a scientific conference.